mineral
Polished agate (likely plume or moss agate)
Chalcedony, microcrystalline quartz (SiO₂), with iron-oxide and possible chlorite inclusions
AI-generated identification · may be incorrectHardness 6.5–7 Mohs; translucent brown, gray, cream, and greenish layers with waxy to vitreous luster. Quartz has trigonal crystal structure, but the specimen is cryptocrystalline and lacks visible cleavage; curved bands and botryoidal contours are characteristic.
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Physical properties
Hardness 6.5–7 Mohs; translucent brown, gray, cream, and greenish layers with waxy to vitreous luster. Quartz has trigonal crystal structure, but the specimen is cryptocrystalline and lacks visible cleavage; curved bands and botryoidal contours are characteristic.
Formation & geological history
Formed when silica-rich groundwater repeatedly filled cavities in volcanic rock, depositing chalcedony and inclusions in layers. Agate formation commonly dates from the Cenozoic to Paleozoic depending on locality.
Uses & applications
Used for cabochons, carvings, ornaments, beads, and collectible polished specimens; its toughness also suits small decorative objects.
Geological facts
The organic-looking patterns are natural mineral growth, not fossils. Brown coloration typically comes from iron oxides, while green areas may reflect chlorite or other minerals.
Field identification & locations
Identify by its waxy translucency, very fine curved banding, conchoidal fracture, and inability to scratch it with a steel knife; quartz should scratch glass. Common sources include Brazil, Uruguay, India, Mexico, and the United States.
